Adaptive differential pulse-code modulation (ADPCM) is used in the context of audio streaming to improve hearing assistance device functionality when streaming from ear-to-ear. ADPCM has a low latency, good quality, a low bitrate, and low computational requirements. However, one drawback to using ADPCM is that it is negatively affected by packet-loss. The negative impact on resulting audio quality when packet-loss occurs with ADPCM is not limited to the dropped packet, but also up to several dozens of milliseconds after the dropped packet.
When using ADPCM, the encoder and the decoder both maintain a certain state based on the encoded signal, which under normal operation and after initial convergence is the same. A packet drop causes the encoder and the decoder states to depart from one another, and the decoder state will take time to converge back to the encoder state once valid data is available again after a drop.
Packet-loss-concealment (PLC) techniques can be used to mitigate the error caused by packet loss. While there are multiple single-channel PLC techniques currently used, they are often slow and costly in terms of instructions per second used, and thus can be infeasible in a hearing assistance device setting.